Note: This work is currently under manuscript preparation so data will not be presented. Prelminary work of this study was presented at the 40th and 43rd Annual Meeting of the American Society of Biomechanics, the slides of which can be viewed from the “Featured Conference Presentations” section. This work was also funded through a NIH R21 grant and a grant through Center for Human Evolution and Devlopment at Penn State.
Overview: It is well-established that exercise during growth increases bone strength. Previous work in mice suggests that bone shape is similarly plastic, but very little research exists on the subject. Bone shape is important, as it acts like a system of levers to help us move. For example, bony protuberances and bone length can influence moment arm lengths, which impacts locomotor capability. The purpose of this study was to investigate if exercise during growth promotes changes to bone shape in addition to bone strength.
For this study, 30 helmeted guineafowl were split into a sedentary (SED) and exercise (EXE) group. SED birds were housed in small pens that restricted their ability to move. EXE birds were housed in large pens, which allowed plenty of movement freedom. EXE birds were also trained for 30 minutes per day, 4x per week, in which they performed short bursts of high-acceleration running. The protocol last for 14 weeks, at which point birds had almost reached skeletal maturity and were sacrificed. Bird carcasses were scanned using a DXA scanner to get a measure of full-body bone mineral content and density. The tarsometatarsus (TMT), analogous to a fused human foot excluding toes, was extracted scanned using a microCT scanner. Bone strength was assessed using cross-sectional properties at 50% of diaphysis length using ImageJ and the BoneJ plug-in. Bone shape was characterized using a 3D array of 159 custom landmarks (created using Avizo and ViewBox) for each TMT. Geometric morphometrics (i.e. general procrustes analysis followed by principal components analysis) were used to characterize differences in bone shape. Other measures of bone shape, such as length and hypotarsus width (analogous to the human heel or tibial tuberosity at the knee but for the ankle), were also taken. Procrustes ANOVA and t-tests on PC1 scores were used to test if groups could be distinguished. T-tests with Bonferonni corrections were used to test for group differences in linear measurements of bone, body size and composition, and bone composition. Geometric morphometrics and statistical analyses were performed in R.
